There is a strong need to increase the capacity and flexibility of photonic transport networks. The evolving telecommunication networks are increasingly focusing on flexibility and reconfigurability, which requires enhanced functionality of photonic integrated circuits (PICs) for optical communications, as well as compact devices. The interest for multi-mode interference (MMI) effects in integrated optics for single-mode transmission systems has recently been increasing. Optical devices based on MMI effects have large optical bandwidth, are polarization insensitive and sustain high fabrication tolerances to mention a few advantages. The operation of MMI waveguide devices is based on the self-imaging principle and is further described in “Optical Multi-Mode Interference Devices Based on Self-Imaging: Principles and Applications” by L. B Soldano and E. C. M. Pennings published in J. of Lightwave Technology, Vol. 13, No. 4 Apr. 1995.
MMI waveguide devices have applications in a number of different areas. For instance, as a wavelength selective switch, as described in “Bragg grating assisted MMIMI coupler for wavelength selective switching” by the present inventor published in Electronics Letters 10th Dec. 1998, Vol. 34, No. 25. In this paper the present inventor describe a novel optical device for wavelength selective switching. The device is based on a Bragg grating assisted MMIMI (multi Mode Interference Michelson Interferometer) coupler.
Another application for a MMI waveguide device is as coupler, as described in the paper “Multimode Interference Couplers with Tuneable Splitting Ratios” by J. Leuthold and C. H. Joyner, published in Proc. ECOC 2000, September, Münich Vol. 3. In this paper the authors present a novel, compact multi-mode interference coupler with tuneable power splitting ratios. The coupler has large tuning ranges and is used to optimise on-off ratios in interferometric devices or even as a switch.
The need to be able to space switch signals in optical telecommunication networks is apparent. Simple space switching of broadband signals allows routing based on for instance available capacity or rerouting around parts of the network currently unavailable.
Prior art optical switches currently face problems with high losses, high cross talk or high requirements on fabrication tolerances. They may also have stability problems or have high power consumption.